A gateway server, point of sale device and protocol are provided for processing financial transactions. A public network interface is configured to couple to a public network and communicate financial authorization requests. The financial authorization requests can include, for example, transaction specific data, a merchant store or location invariant and a supplemental header. A gateway processor processes the financial transaction authorization requests and couples to a financial network interface configured to couple to at least one financial network. The gateway provides a response to the point of sale device based upon data received from the financial network and the authorization request.